The present invention is directed to a improved laminate of inorganic sheet and polyester polymer, preferably a laminate of two inorganic sheets separated by a polyester polymer layer. Such laminates are useful in transformers and other electrical devices wherein the laminate serves as dielectric insulation material. Such laminates need to have folding endurance and toughness. Any improvement in the internal adhesion of the laminate or the tear or elongation at break properties of such laminates is desirable.